1. Field of the Invention
The present invention relates to an electronic sphygmomanometer, and, in particular, to a constant rate air-bleed adjustment device for a sphygmomanometer whereby the pressure in a cuff can be easily adjusted to drop at a substantially uniform rate.
2. Description of the Prior Art
Conventional electronic sphygmomanometers wherein a cuff is pressurized by means of a battery-driven electric pump, a pulse and the air pressure inside the cuff are detected by a pressure sensor, and the systolic and diastolic blood pressure values of a patient whose blood pressure is being measured are obtained and displayed on a digital display device are in widespread use.
In this type of electronic sphygmomanometer, a constant rate air-bleed device is used in order to reduce the pressure of the air inside the cuff at a constant rate.
FIG. 1 shows one example of a constant rate air-bleed valve used with a conventional electronic sphygmomanometer.
In this constant rate air-bleed valve, a flange section 2a of a tubular member 2, as shown in FIG. 2, is insertedly pressed into an inner section of an air-bleed valve casing 1 with a pressure side part la by means of a nut 3, and, in addition, a regulating member 4 is screwed into the nut 3 (as, for example, in Japanese Patent Publication 63-14809).
The flange section 2a is provided on one end of the tubular member 2, as shown in FIG. 2, and on the outer peripheral side surface of the tubular member 2, a slit 2b is provided, extending in the longitudinal direction from the flange section 2a. An air-bleed hole 4a is formed in the center of the regulating member 4, and an end 4b of the regulating member 4 contacts the flange section 2a of the tubular member 2. The rate of pressure reduction is regulated by screwing in the regulating member 4, thus increasing the pressure on the the tubular member 2 in the thrust direction, so that the amount of open area of the longitudinal slit 2b increases, corresponding to this pressure.
Accordingly, in this type of conventional constant-rate air-bleed valve, because the longitudinal slit 2a is provided in the tubular member 2, a uniform length in the longitudinal direction is absolutely necessary to obtain good characteristics. In addition, because pressure must be added in the thrust direction, the length of the regulating section in the longitudinal direction must be great. Also, to ensure that the regulating section is airtight, the regulating section must also be large in the radial direction. This gives rise to the drawback that the overall air-bleed valve must be large.